Medical devices for delivery of therapeutic agents

ABSTRACT

The present invention is generally directed to medical devices, and more specifically to medical devices that are at least partially insertable or implantable into the body of a patient. The medical devices generally comprise (a) a therapeutic agent, more typically, a high-molecular-weight therapeutic agent, and (b) at least one polymeric layer, which typically acts to control the release of the therapeutic agent from the medical device. Also disclosed herein are methods of making such medical devices.

FIELD OF THE INVENTION

The present invention relates to implantable or insertable medicaldevices, such as intraluminal stents, that release therapeutic agents.The medical devices of the present invention are particularlyappropriate for the release of high molecular weight therapeutic agents,such as DNA.

BACKGROUND OF THE INVENTION

Percutaneous transluminal coronary angioplasty (“PTCA” or “angioplasty”)procedures have been performed for many years as an adjunct tocorrecting vascular disease in patients. Angioplasty procedures involvethe insertion, through the vascular system, of a catheter having aballoon that is placed across a lesion or blockage in a coronary artery.The balloon is then inflated to compress the lesion or blockage againstthe arterial walls, thereby opening the artery for increased blood flow.

In some cases, however, the goal of the angioplasty procedure isdefeated at least in part by a complete or partial reclosure of theartery at or near the compressed lesion or blockage. Two mechanisms arebelieved to be principally responsible for reclosure of the artery. Thefirst mechanism is recoil, which is a mechanical process involving theelastic rebound of the compressed lesion or blockage. The secondmechanism is restenosis, which is believed to be caused by proliferationof the smooth muscle cells present in the artery walls near the lesionor blockage. Restenosis can occur over a period of several weeks ormonths after the PTCA procedure.

Many different methods have been employed to limit the effect ofrestenosis, including radiation treatments and various drug therapies,delivered locally and systemically, to slow proliferation of the smoothmuscle cells. Recoil of the arterial walls can be prevented by usingstents, which can be temporarily or permanently deployed within theartery to mechanically maintain patency of the artery. Stents are veryeffective at carrying out this task, but they may also irritate thecontacting arterial walls, which may in turn encourage additionalrestenosis.

Gene therapy has been used for diverse medical purposes, includingslowing proliferation of smooth muscle cells. Genes are usuallydelivered into a patient's cells through a vector, such as a retroviralvector, whose DNA is genetically engineered to include a desired DNAsequence. Alternatively, nonviral gene transfer methods can be used,such as plasmid DNA vectors, along with polymeric carriers, DNAcondensing agents, lipofection and receptor mediated delivery vectors.

In connection with angioplasty, incorporation of appropriate DNAmolecules into the coronary artery walls near the treatment site can bebeneficial to inhibit restenosis. A polymer-coated stent can be used asthe delivery vehicle for the DNA, in addition to maintaining patency ofthe artery following PTCA.

However, effective delivery of high-molecular-weight therapeutic agents,such as DNA and any associated vector, can entail large amounts oftherapeutic agent and long delivery times. Large amounts of polymericmaterial provided as a coating on the stent may, therefore, be requiredto adequately incorporate the therapeutic agent and ensure controlledand extended release of the therapeutic agent over a required period oftime. Consequently, the polymeric coating may become relatively thick,increasing the susceptibility, during expansion of the stent, tocracking of the coating. Such cracking can reduce the effectiveness ofthe coating to deliver the therapeutic agent therefrom, among otherconsequences. Moreover, because some medical devices such as stents havelimited surface areas for disposition of a polymer coating, it would bedesirable to provide a coating that actually enhances the uptake of thetherapeutic agent by the tissue of interest.

The manufacture of medical devices with high-molecular-weighttherapeutic agents in polymer matrices can also present processingdifficulties. For example, relatively high shear stresses are commonlyencountered while processing a mixture of a polymeric material and atherapeutic agent. In the case of certain high-molecular-weighttherapeutic agents such as polynucleotides (e.g., plasmids), forexample, these shear stresses can, in turn, disrupt the conformationaland/or structural integrity of the therapeutic agent.

Moreover, certain biostable polymers that are highly biocompatible(e.g., polystyrene-polyisobutylene copolymers) may in some cases provideinsufficient mass transport therethrough of high-molecular-weighttherapeutic agents after deployment, limiting their utility in medicaldevices that deliver such agents.

Accordingly, there is a need for coatings for stents and other medicaldevices that release high-molecular-weight therapeutic agents in acontrolled fashion over a period of time and do not suffer from theforegoing and other disadvantages. The coatings should, therefore,contain a therapeutically effective amount of high-molecular-weighttherapeutic agent and provide adequate control of the release of thattherapeutic agent. In addition, in the case of expandable medicaldevices such as stents and balloons, the coatings should resist crackingthat may occur during expansion of the medical device. Moreover, theconformational and structural integrity of high-molecular-weighttherapeutic agents such as DNA should be preserved to the greatestextent possible during manufacture of the medical device.

SUMMARY OF THE INVENTION

These and other needs are met by the present invention.

According to one aspect of the present invention, a medical device isprovided, at least a portion of which is insertable or implantable intothe body of a patient. The medical device comprises: (a) a plasmid DNAlayer, which comprises plasmid DNA; and (b) a polymeric covering layerdisposed over the plasmid DNA layer.

Examples of implantable or insertable medical devices include catheters,balloons, filters, coils, clips, slings, and intraluminal stents, forinstance, vascular stents.

The plasmid DNA layer may be applied in a number of ways, for example,by dipping at least a portion of the medical device into a solutioncomprising the plasmid DNA.

The polymeric covering layer can be, for example, a biostable polymericcovering layer or a biodisintegrable polymeric covering layer.

Examples of biostable polymeric covering layers include those thatcomprise one or more of the following: polyolefin polymers andcopolymers; ethylenic copolymers; polyurethane polymers and copolymers;metallocene catalyzed polyethylene polymers and copolymers; ionomers;polyester-ether polymers and copolymers; polyamide-ether polymers andcopolymers; and silicone polymers and copolymers.

The biostable polymeric covering layer can comprise, for example, ablock copolymer comprising at least two polymeric blocks A and B,wherein A is a polyolefin block and B is a vinyl aromatic block. Forexample, A can be a polyolefin block of the general formula—(CRR′—CH₂)_(n)—, where R and R′ are linear or branched aliphatic groupsor cyclic aliphatic groups and B can be is a vinyl aromatic polymerblock. As another example, A can be a polyolefin block that comprisesone or more monomers selected from ethylene, butylene and isobutylene,and B can be a vinyl aromatic polymer block that comprises one or moremonomers selected from styrene and α-methylstyrene.

Examples of biodisintegrable polymeric covering layers include thosethat comprise one or more of the following: lactic acid polymers andcopolymers, glycolic acid polymers and copolymers, trimethylenecarbonate polymers and copolymers, caprolactone polymers and copolymers,hyaluronic acid polymers and copolymers, hydroxybutyrate polymers andcopolymers, and tyrosine-based polymers and copolymers.

The biodisintegrable polymeric covering layer can comprise, for example,(a) hyaluronic acid polymers, (b) copolymers of lactic acid and glycolicacid, and/or (c) tyrosine-derived polycarbonates.

According to another aspect of the present invention, a medical deviceis provided, at least a portion of which is insertable or implantableinto the body of a patient. The medical device comprises (a) atherapeutic agent containing layer. which comprises ahigh-molecular-weight therapeutic agent; and (b) a polymeric coveringlayer disposed over the high-molecular-weight-therapeutic-agent layer.The polymeric covering layer comprises one or more polymers selectedfrom (i) a block copolymer comprising at least two polymeric blocks Aand B, wherein A is a polyolefin block and wherein B is a vinyl aromaticblock, (ii) a polymer or copolymer of lactic acid, (iii) a polymer orcopolymer of glycolic acid, and (iv) a tyrosine-based polymer orcopolymer.

The therapeutic agent containing layer may be applied in a number ofways, for example, by dipping at least a portion of the medical deviceinto a solution comprising the high-molecular-weight therapeutic agent.

Examples of high-molecular-weight therapeutic agents include: (a)polysaccharide therapeutic agents having a molecular weight greater than1,000; (b) polypeptide therapeutic agents having a molecular weightgreater than 10,000; and (c) polynucleotides having a molecular weightgreater than 2,000, for instance, plasmid DNA.

According to another aspect of the present invention, a medical deviceis provided, at least a portion of which is insertable or implantableinto the body of a patient. The medical device comprises (a) polymericlayer comprising a removable component as well as (i) a block copolymercomprising at least two polymeric blocks A and B, wherein A is apolyolefin block and B is a vinyl aromatic block and/or (ii) atyrosine-based polymer or copolymer; and (b) a high-molecular-weighttherapeutic agent disposed below or within the polymeric layer.

The removable component can be, for example, a leachable material, suchas polyethylene glycols, polyalkylene oxides (e.g., polyethylene oxideand copolymers of polyethylene oxide and polypropylene oxide),polyhydroxyethylmethacrylates, polyvinylpyrrolidones, polyacrylamide andits copolymers, liposomes, proteins, peptides, salts, sugars,polysaccharides, polylactides, cationic lipids, detergents,polygalactides, polyanhydrides, polyorthoesters and their copolymers,and soluble cellulosics.

According to another aspect of the present invention, a medical deviceis provided, at least a portion of which is insertable or implantableinto the body of a patient. The medical device comprises (a) a polymericlayer comprising a polymer and a plasticizer; and (b) ahigh-molecular-weight polynucleotide therapeutic agent (e.g., plasmidDNA) disposed below or within the polymeric layer.

The plasticizer can be, for example, glycerol, triacetyl glycerin,ethylene glycol, triethylene glycol, polyethylene glycol, propyleneglycol, polyalkylene oxides (e.g., polyethylene oxide and copolymers ofpolyethylene oxide and polypropylene oxide), citric acid esters, sebacicacid esters, phthalic acid esters, and silicone fluid.

According to another aspect of the present invention, a medical deviceis provided, at least a portion of which is insertable or implantableinto the body of a patient. The medical device comprises a multi-layercoating that covers at least a portion of the medical device. Themulti-layer coating further comprises (a) one or more therapeutic agentcontaining layers comprising a therapeutic agent and (b) one or morepolymeric layers comprising a polymer, wherein the one or more polymericlayers have a composition gradient in a direction normal to the surfaceof the coating.

The therapeutic agent can be, for example, a high-molecular-weighttherapeutic agent.

The one or more therapeutic agent containing layers can be disposed, forexample, beneath the one or more polymeric layers. In an alternativeembodiment, a plurality of therapeutic agent containing layers aredisposed in an alternating configuration with a plurality of polymerlayers.

In some embodiments, the composition gradient is provided within asingle polymeric layer. In others, the composition gradient is providedwithin a plurality of polymeric layers (e.g., 2, 3, 4, 5 or morepolymeric layers).

The composition gradient can comprise, for example, (a) a gradient inporosity, (b) a gradient in polymer composition, for example, a gradientin the relative proportions of two or more monomer species within acopolymer or a gradient in the relative proportions of two or morepolymers within a polymer blend (for example, the relative proportionsof a hydrophobic polymer, such as styrene-isobutylene copolymer, and ahydrophilic polymer, such as a styrene-ethylene oxide copolymer), (c) agradient in the composition of a leachable species, (d) a gradient inthe composition of an acidic species, (e) a gradient in the compositionof a basic species and/or (f) a gradient in the composition of an ionicspecies.

One advantage of the present invention is that polymer coated medicaldevices such as stents, containing therapeutic agents, includinghigh-molecular-weight therapeutic agents such as DNA, can be provided inwhich the rate of release of the therapeutic agents is adequatelyregulated so as to provide a therapeutically effective amount of suchagent over a desired period of time.

Another advantage of the present invention is that polymer coatedmedical devices, such as stents, containing therapeutic agents,including high-molecular-weight therapeutic agents such as DNA, can beprovided in which the polymer resists cracking upon expansion of themedical device.

Another advantage of the present invention is that medical devices suchas stents, containing therapeutic agents, includinghigh-molecular-weight therapeutic agents such as DNA, can be providedwherein the structural integrity of the therapeutic agent is notsubstantially disrupted during medical device manufacture.

Yet another advantage of the present invention is that medical devicessuch as stents, containing therapeutic agents, and particularlyhigh-molecular-weight therapeutic agents such as DNA, can be provided inwhich the uptake of the therapeutic agent by the targeted tissue isenhanced.

These and other embodiments and advantages of the invention will becomeapparent from the following detailed description, and the accompanyingdrawings, which illustrate by way of example the features of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a stent with a polymer coating,according to an embodiment of the invention.

FIG. 2 is a schematic diagram of a stent with a polymer coating,according to an embodiment of the invention.

FIG. 3 is a schematic diagram of a stent with a polymer coating,according to an embodiment of the invention.

FIG. 4 is a graph of DNA release as a function of time forbiodisintegrable coatings, according to an embodiment of the invention.

FIG. 5 is a graph of DNA release as a function of time forbiodisintegrable coatings, according to an embodiment of the invention.

FIG. 6 is a graph of coating dissolution as a function of time forbiodisintegrable coatings, according to an embodiment of the invention.

FIG. 7 is a graph of coating dissolution as a function of time forbiodisintegrable coatings, according to an embodiment of the invention.

FIG. 8 is a graph of coating dissolution as a function of time forbiodisintegrable coatings, according to an embodiment of the invention.

FIG. 9 is a graph of DNA release as a function of time forbiodisintegrable coatings, according to an embodiment of the invention.

FIG. 10 is a graph of DNA release as a function of time forbiodisintegrable coatings, according to an embodiment of the invention.

FIG. 11 is a graph of DNA adsorption as a function of DNA concentration,according to an embodiment of the invention.

FIG. 12 is a graph of DNA release as a function of time forbiodisintegrable coatings, according to an embodiment of the invention.

FIG. 13 is a photograph of a stent after implantation in a rabbit iliacartery, according to an embodiment of the invention.

FIG. 14 is a graph of DNA release as a function of time for a biostablecoating, according to an embodiment of the invention.

FIG. 15 is a graph of dextran release as a function of time forbiostable coatings, according to an embodiment of the invention.

FIG. 16 is a graph of dextran release as a function of time forbiostable coatings, according to an embodiment of the invention.

FIG. 17 is a photograph of a biostable coating material after NaClextraction in PBS, according to an embodiment of the invention.

FIG. 18 is a graph of DNA release as a function of time for biostablecoatings, according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The various embodiments of the present invention are directed toimplantable or insertable medical devices in which a polymer coatinglayer is used to regulate local delivery of a therapeutic agent, andtypically a high-molecular-weight therapeutic agent, as defined below.

Localized delivery of a therapeutic agent from an implantable orinsertable medical device is advantageous, because higher localconcentrations of the therapeutic agent and/or more regulated deliverythereof can be achieved than with systemic administration. Consequently,increased cellular uptake of the therapeutic agent and therapeuticefficacy can be achieved with localized delivery, as opposed to systemicdelivery of the therapeutic agent.

For example, systemic administration of several doses of therapeuticagent typically results in peaks and troughs in the level ofconcentration received by the tissue. In some cases, the peaks may behigher than a maximum desired level, leading to undesirable sideeffects, for example, and the troughs may be lower than a minimumeffective level for the therapeutic agent. On the other hand, localadministration of the therapeutic agent, for example, via a coatedstent, can provide a concentration level of delivered agent that remainswithin a therapeutically effective range for a longer period of time.

The present invention is applicable to implantable or insertable medicaldevices of any shape or configuration. Examples of medical devicesappropriate for the practice of the present invention includeintraluminal catheters (including vascular catheters such as ballooncatheters), guide wires, balloons, filters (e.g., vena cava filters),stents, stent grafts, cerebral stents, cerebral aneurysm filler coils(including metal coils and GDC—Guglilmi detachable coils), clips,slings, vascular grafts, myocardial plugs, pacemaker leads and heartvalves.

More specific examples of medical devices for the practice of thepresent invention include intraluminal stents such as endovascular,biliary, tracheal, gastrointestinal, urethral, ureteral, esophageal andcoronary vascular stents. The intraluminal stents of the presentinvention may be, for example, balloon-expandable or self-expandable.Thus, although certain embodiments of the present invention will bedescribed herein with reference to vascular stents, the presentinvention is applicable to other medical devices, including other typesof stents.

In general, stents for use in connection with the present inventiontypically comprise a plurality of apertures or open spaces betweenmetallic filaments (including fibers and wires), segments or regions.Typical structures include: an open-mesh network comprising one or moreknitted, woven or braided metallic filaments; an interconnected networkof articulable segments; a coiled or helical structure comprising one ormore metallic filaments; and, a patterned tubular metallic sheet (e.g.,a laser cut tube).

FIGS. 1 and 3 illustrate two embodiments of polymer coated endovascularstents 10 according to the present invention. FIG. 2 shows a detailedenlargement of a portion of a polymer-coated stent that is similar indesign to that shown in FIG. 1. Each stent 10 can be, for example, acoronary stent sized to fit in the blood vessel of a patient, which isformed from a plurality of structural elements 12. The construction ofeach stent 10 permits the stent 10 to be introduced into the vascularsystem in a collapsed configuration, minimizing the diameter of thestent 10. Each stent 10 can then expand to an expanded position at thedesired location within the blood vessel of the patient. The structuralelements 12 of each stent 10 form a conventional frame, such as tubularshape, and permits the stent 10 to self-expand or to expand to thedesired shape after an expansive force is applied, for example, by theexpansion of a balloon within the stent.

A coating 16 is applied on the surface of each stent 10. According tothe present invention, coating 16 can include either a biostable orbiodisintegrable polymer as described more fully below, which contains,or is provided as a coating over, a therapeutic agent. The therapeuticagent is released in a controlled manner after introduction of the stent10 into the body of the patient. As one specific example, in the case ofhigh-molecular-weight therapeutic agent such as plasmid DNA, a typicalcoronary stent can have a uniform coating of approximately 1,000micrograms in weight or more, which contains up to 100 micrograms ofplasmid DNA or more.

The structural elements 12 of each stent 10 form windows 14 such thatthe stent 10 does not have a continuous outer shell. Windows 14 aregenerally present in most stent configurations, although the specificdetails of the shape of structural elements 12 and the construction ofstent 10 can vary as can be seen, for example, from FIGS. 1-3. Eachstent 10 can thus be coated with polymeric coating 16 such that windows14 remain free of coating. Alternatively, each stent 10 can be coveredby coating 16 such that a layer or web of coating (not shown) alsocovers the windows 14 between elements 12. For certain embodiments, itis beneficial that the windows 14 be left free of a covering. Theunobstructed windows: (a) allow a freer exchange of nutrients betweenthe inner walls of the vessel and the fluid flowing through the vessel,such as blood flowing in an artery and (b) do not block flow to vesselside-branches. In alternate embodiments, the material filling thewindows is sufficiently porous to allow exchange of nutrients andoxygen.

Various embodiments of the invention can be implemented by dipping amedical device of interest into a solution (e.g., a solution containinga polymer and a high-molecular-weight therapeutic agent). In suchembodiments, it may be desirable to employ a stent holder, such as thoseknown in the art, which facilitates placing the stent in solution andsubsequently removing and spinning the stent to remove excess solution.

Typical sites for placement of the medical devices of the presentinvention include the coronary and peripheral vasculature (collectivelyreferred to herein as the vasculature), esophagus, trachea, colon,gastrointestinal tract, biliary tract, urinary tract, prostate, brainand surgical sites. Where the medical device is inserted into thevasculature, for example, the therapeutic agent is may be released to ablood vessel wall adjacent the device, and may also be released todownstream vascular tissue as well.

After the medical devices of the present invention are deployed at asuitable site, the therapeutic agent is released and delivered locallyto tissue adjacent the medical device. Depending upon the application,various release profiles can be provided in accordance with the presentinvention including: (a) 50% release (i.e., 50% of the total releasefrom the medical device that occurs over the prescribed course ofimplantation/insertion) occurring during a period of 15-60 minutes afterimplantation/insertion, (b) 50% release occurring over a period of 1-6hours, (b) 50% release occurring over a period of 6-24 hours, (c) 50%release occurring over a period of 24-96 hours (4 days), (d) 50% releaseoccurring over a period of 4-14 days, (e) 50% release occurring over aperiod of 2-8 weeks, (f) 50% release occurring over a period of 8-32weeks.

Typical subjects (also referred to herein as “patients”) are vertebratesubjects (i.e., members of the subphylum cordata), including, mammalssuch as cattle, sheep, pigs, goats, horses, dogs, cats and humans.

“Therapeutic agents”, “pharmaceutically active agents”,“pharmaceutically active materials”, “drugs” and other related terms maybe used interchangeably herein and include genetic therapeutic agents,non-genetic therapeutic agents, and cells.

Exemplary non-genetic therapeutic agents include: (a) anti-thromboticagents such as heparin, heparin derivatives, urokinase, and PPack(dextrophenylalanine proline arginine chloromethylketone); (b)anti-inflammatory agents such as dexamethasone, prednisolone,corticosterone, budesonide, estrogen, sulfasalazine and mesalamine; (c)antineoplastic/antiproliferative/anti-mitotic agents such as paclitaxel,5-fluorouracil, cisplatin, vinblastine, vincristine, epothilones,endostatin, angiostatin, angiopeptin, monoclonal antibodies capable ofblocking smooth muscle cell proliferation, and thymidine kinaseinhibitors; (d) anesthetic agents such as lidocaine, bupivacaine andropivacaine; (e) anti-coagulants such as D-Phe-Pro-Arg chloromethylketone, an RGD peptide-containing compound, heparin, hirudin,antithrombin compounds, platelet receptor antagonists, anti-thrombinantibodies, anti-platelet receptor antibodies, aspirin, prostaglandininhibitors, platelet inhibitors and tick antiplatelet peptides; (f)vascular cell growth promoters such as growth factors, transcriptionalactivators, and translational promotors; (g) vascular cell growthinhibitors such as growth factor inhibitors, growth factor receptorantagonists, transcriptional repressors, translational repressors,replication inhibitors, inhibitory antibodies, antibodies directedagainst growth factors, bifunctional molecules consisting of a growthfactor and a cytotoxin, bifunctional molecules consisting of an antibodyand a cytotoxin; (h) protein kinase and tyrosine kinase inhibitors(e.g., tyrphostins, genistein, quinoxalines); (i) prostacyclin analogs;(j) cholesterol-lowering agents; (k) angiopoietins; (I) antimicrobialagents such as triclosan, cephalosporins, aminoglycosides andnitrofurantoin; (m) cytotoxic agents, cytostatic agents and cellproliferation affectors; (n) vasodilating agents; and (o) agents thatinterfere with endogenous vasoactive mechanisms.

Exemplary genetic therapeutic agents include anti-sense DNA and RNA,oligo decoys, as well as DNA coding for: (a) anti-sense RNA, (b) tRNA orrRNA to replace defective or deficient endogenous molecules, (c)angiogenic factors including growth factors such as acidic and basicfibroblast growth factors, vascular endothelial growth factor, epidermalgrowth factor, transforming growth factor α and β, platelet-derivedendothelial growth factor, platelet-derived growth factor, tumornecrosis factor α, hepatocyte growth factor and insulin-like growthfactor, (d) cell cycle inhibitors including CD inhibitors, and (e)thymidine kinase (“TK”) and other agents useful for interfering withcell proliferation. Also of interest is DNA encoding for the family ofbone morphogenic proteins (“BMP's”), including BMP-2, BMP-3, BMP-4,BMP-5, BMP-6 (Vgr-1), BMP-7 (OP-1), BMP-8, BMP-9, BMP-10, BMP-11,BMP-12, BMP-13, BMP-14, BMP-15, and BMP-16. Currently beneficial BMP'sare any of BMP-2, BMP-3, BMP-4, BMP-5, BMP-6 and BMP-7. These dimericproteins can be provided as homodimers, heterodimers, or combinationsthereof, alone or together with other molecules. Alternatively, or inaddition, molecules capable of inducing an upstream or downstream effectof a BMP can be provided. Such molecules include any of the “hedgehog”proteins, or the DNA's encoding them.

Cells include cells of human origin (autologous or allogeneic),including stem cells and platelets, or from an animal source(xenogeneic), which can be genetically engineered if desired to deliverproteins of interest.

Numerous therapeutic agents, not necessarily exclusive of those listedabove, have been identified as candidates for vascular treatmentregimens, for example, as agents targeting restenosis. Such agents areappropriate for the practice of the present invention and include one ormore of the following: (a) Ca-channel blockers includingbenzothiazapines such as diltiazem and clentiazem, dihydropyridines suchas nifedipine, amlodipine and nicardapine, and phenylalkylamines such asverapamil, (b) serotonin pathway modulators including: 5-HT antagonistssuch as ketanserin and naffidrofuryl, as well as 5-HT uptake inhibitorssuch as fluoxetine, (c) cyclic nucleotide pathway agents includingphosphodiesterase inhibitors such as cilostazole and dipyridamole,adenylate/guanylate cyclase stimulants such as forskolin, as well asadenosine analogs, (d) catecholamine modulators including α-antagonistssuch as prazosin and bunazosine, β-antagonists such as propranolol andα/β-antagonists such as labetalol and carvedilol, (e) endothelinreceptor antagonists, (f) nitric oxide donors/releasing moleculesincluding organic nitrates/nitrites such as nitroglycerin, isosorbidedinitrate and amyl nitrite, inorganic nitroso compounds such as sodiumnitroprusside, sydnonimines such as molsidomine and linsidomine,nonoates such as diazenium diolates and NO adducts of alkanediamines,S-nitroso compounds including low molecular weight compounds (e.g.,S-nitroso derivatives of captopril, glutathione and N-acetylpenicillamine) and high molecular weight compounds (e.g., S-nitrosoderivatives of proteins, peptides, oligosaccharides, polysaccharides,synthetic polymers/oligomers and natural polymers/oligomers), as well asC-nitroso-compounds, O-nitroso-compounds, N-nitroso-compounds andL-arginine, (g) ACE inhibitors such as cilazapril, fosinopril andenalapril, (h) ATII-receptor antagonists such as saralasin and losartin,(i) platelet adhesion inhibitors such as albumin and polyethylene oxide,(j) platelet aggregation inhibitors including aspirin and thienopyridine(ticlopidine, clopidogrel) and GP IIb/IIIa inhibitors such as abciximab,epitifibatide and tirofiban, (k) coagulation pathway modulatorsincluding heparinoids such as heparin, low molecular weight heparin,dextran sulfate and β-cyclodextrin tetradecasulfate, thrombin inhibitorssuch as hirudin, hirulog, PPACK(D-phe-L-propyl-L-arg-chloromethylketone)and argatroban, FXa inhibitors such as antistatin and TAP (tickanticoagulant peptide), Vitamin K inhibitors such as warfarin, as wellas activated protein C, (1) cyclooxygenase pathway inhibitors such asaspirin, ibuprofen, flurbiprofen, indomethacin and sulfinpyrazone, (m)natural and synthetic corticosteroids such as dexamethasone,prednisolone, methprednisolone and hydrocortisone, (n) lipoxygenasepathway inhibitors such as nordihydroguairetic acid and caffeic acid,(o) leukotriene receptor antagonists, (p) antagonists of E- andP-selectins, (q) inhibitors of VCAM-1 and ICAM-1 interactions, (r)prostaglandins and analogs thereof including prostaglandins such as PGE1and PGI2 and prostacyclin analogs such as ciprostene, epoprostenol,carbacyclin, iloprost and beraprost, (s) macrophage activationpreventers including bisphosphonates, (t) HMG-CoA reductase inhibitorssuch as lovastatin, pravastatin, fluvastatin, simvastatin andcerivastatin, (u) fish oils and omega-3-fatty acids, (v) free-radicalscavengers/antioxidants such as probucol, vitamins C and E, ebselen,trans-retinoic acid and SOD mimics, (w) agents affecting various growthfactors including FGF pathway agents such as bFGF antibodies andchimeric fusion proteins, PDGF receptor antagonists such as trapidil,IGF pathway agents including somatostatin analogs such as angiopeptinand ocreotide, TGF-β pathway agents such as polyanionic agents (heparin,fucoidin), decorin, and TGF-β antibodies, EGF pathway agents such as EGFantibodies, receptor antagonists and chimeric fusion proteins, TNF-αpathway agents such as thalidomide and analogs thereof, Thromboxane A2(TXA2) pathway modulators such as sulotroban, vapiprost, dazoxiben andridogrel, as well as protein tyrosine kinase inhibitors such astyrphostin, genistein and quinoxaline derivatives, (x) MMP pathwayinhibitors such as marimastat, ilomastat and metastat, (y) cell motilityinhibitors such as cytochalasin B, (z) antiproliferative/antineoplasticagents including antimetabolites such as purine analogs (e.g.,6-mercaptopurine or cladribine, which is a chlorinated purine nucleosideanalog), pyrimidine analogs (e.g., cytarabine and 5-fluorouracil) andmethotrexate, nitrogen mustards, alkyl sulfonates, ethylenimines,antibiotics (e.g., daunorubicin, doxorubicin), nitrosoureas, cisplatin,agents affecting microtubule dynamics (e.g., vinblastine, vincristine,colchicine, paclitaxel and epothilone), caspase activators, proteasomeinhibitors, angiogenesis inhibitors (e.g., endostatin, angiostatin andsqualamine), rapamycin, cerivastatin, flavopiridol and suramin, (aa)matrix deposition/organization pathway inhibitors such as halofuginoneor other quinazolinone derivatives and tranilast, (bb)endothelialization facilitators such as VEGF and RGD peptide, (cc) bloodrheology modulators such as pentoxifylline, and (dd) endothelial-cellspecific mitogens.

Further therapeutic agents appropriate for the practice of the presentinvention, again not necessarily exclusive of those listed above, arealso disclosed in U.S. Pat. No. 5,733,925 assigned to NeoRx Corporation,the entire disclosure of which is incorporated by reference.

The present invention is especially useful in deliveringhigh-molecular-weight therapeutic agents, which are defined herein toinclude therapeutic agents having a molecular weight greater than 500,typically greater than 1,000, more typically greater than 2,000, oragents which contain one or more components having such molecularweights. Examples are polysaccharide therapeutic agents having amolecular weight greater than 1,000; polypeptide therapeutic agentshaving a molecular weight greater than 10,000; polynucleotides,including antisense polynucleotides, having a molecular weight greaterthan 2,000, gene-encoding polynucleotides, including plasmids, having amolecular weight greater than 500,000; viral and non-viral particleshaving a diameter greater than about 50 nanometers, and cells.

A “polynucleotide” is a nucleic acid polymer. A polynucleotide caninclude both double- and single-stranded sequences, and can includenaturally derived and synthetic DNA sequences. The term also includessequences that include any of the known base analogs of DNA and RNA, andincludes modifications, such as deletions, additions and substitutions(generally conservative in nature) to native sequences. In someembodiments of the invention, the polynucleotide can be, for example, anantisense polynucleotide. In others, polynucleotide can be, for example,of transfection unit length, which is typically on the order of about 1kb or greater.

Typical polynucleotide therapeutic agents include the genetictherapeutic agents specifically listed above, and more generally includeDNA encoding for various polypeptide and protein products includingthose previously listed. Some additional examples of polynucleotidetherapeutic agents include DNA encoding for the following: cytokinessuch as colony stimulating factors (e.g., granulocyte-macrophagecolony-stimulating factor), tumor necrosis factors (e.g., fas ligand)and interleukins (e.g., IL-10, an anti-inflammatory interleukin), aswell as protease inhibitors, particularly serine protease inhibitors(e.g., SERP-1), tissue inhibiting metalloproteinases (e.g., TIMP-1,TIMP-2, TIMP-3, TIMP-4), monocyte chemoattractant proteins (e.g.,MCP-1), protein kinase inhibitors including cyclin-dependent kinaseinhibitors (e.g., p27, p21), endogenous and inducible nitric oxidesynthase, CO-generating enzymes, such as hemoxygenases, which catalyzethe oxidation of heme into the biologically active molecules ironbiliverdin and CO (e.g., HOI-1), antiproliferative compounds, such ashKIS in a transdominant mutant peptide form, which are capable ofinterfering with the ability of endogenous hKIS to phosphorylate p27thereby enhancing cell cycle arrest, as well as derivatives of theforegoing.

Vectors of interest for delivery of polynucleotide therapeutic agentsinclude (a) viral vectors such as adenovirus, adenoassociated virus andlentivirus, and (b) non-viral vectors such as DNA plasmid, along withcondensing agents, receptor mediated delivery vectors, polymericcarriers, lipids (including cationic lipids), and liposomes.

The term “polypeptide” refers to a polymer of amino acid residues. Bothfull-length proteins and fragments thereof are encompassed by thedefinition. The terms also include modifications, such as deletions,additions and substitutions (generally conservative in nature), tonative sequence. Exemplary polypeptides include any of thepolypeptides/proteins listed in the preceding paragraphs.

The term “polysaccharide” refers to a polymer of monosaccharideresidues. Typical polysaccharides include any of the polysaccharideslisted in the preceding paragraphs. Low and high molecular weightheparin and dextran, including derivatives of the same, for example,dextran sulfate salts and dextran-metal complexes such as dextran-ironcomplex, are some exemplary polysaccharides.

Hybrids of the above high-molecular-weight therapeutics (e.g.,DNA/protein hybrids and polysaccharide/protein hybrids) are also withinthe scope of the present invention.

Some specific classes of high-molecular-weight therapeutic agents areanti-proliferative agents, anti-inflammatory agents, anti-thromboticagents, lipid mediators, vasodilators, anti-spasm agents, remodelingagents, endothelial-cell specific mitogens, as well as nucleotidesequences (which may further include an associated delivery vector)encoding for therapeutic agents having any one or combination of thesetherapeutic effects. Examples include plasmids that encode anantiproliferative protein within the arterial walls to help prevent arecurring blockage due to restenosis, anti-inflammatory proteins andanti-thrombotic polysaccharides designed to prevent blood clotting.

It is noted that multiple therapeutic agents can be used simultaneouslyin connection with the present invention. Moreover, even in embodimentscentered on the use of high-molecular-weight therapeutic agents, themedical device may optionally contain other therapeutic agents that aresuitable for localized delivery from implantable or insertable medicaldevices, even though these optional therapeutic agents are nothigh-molecular-weight therapeutic agents. Numerous examples of suchother therapeutic agents are described above.

The amount of therapeutic agent that is provided in connection with thevarious embodiments of the present invention is readily determined bythose of ordinary skill in the art and ultimately depends upon thecondition to be treated, the nature of the therapeutic agent itself, theavenue by which the medical device is administered to the intendedsubject, and so forth.

In some embodiments of the present invention, the therapeutic agent isincorporated within a polymer layer provided as a coating on the medicaldevice. The polymer layer hence acts as a depot for the therapeuticagent, releasing the therapeutic agent in a controlled manner once themedical device has been positioned within the patient's body.

In other embodiments, a polymer layer acts as a barrier layer to controlthe passage of the therapeutic agent. In such embodiments, thetherapeutic agent is positioned under the barrier layer. As an example,the barrier layer can be disposed over a layer of therapeutic agentwhich has been disposed directly onto the surface of the medical deviceor onto the surface of a polymeric coating layer previously applied ontothe surface of the medical device. As another example, the barrier layercan be disposed over a layer that contains a material in addition to thetherapeutic agent, for example, a polymer matrix layer within which thetherapeutic agent is incorporated.

Polymers appropriate for the practice of the present invention include avariety of biocompatible polymers known in the art to be suitable foruse in implantable or insertable medical devices. The biocompatiblepolymer may be biostable or biodisintegrable. By “biostable” is meant apolymer that does not substantially disintegrate (i.e., deteriorate) invivo. Thus, a biostable polymer is one that maintains its structuralintegrity, i.e., is substantially inert, in the presence of aphysiological environment. “Biodisintegrable” polymers are those thatundergo substantial deterioration in vivo, and include soluble polymers,bioerodable polymers and biodegradable polymers.

Exemplary biocompatible biostable polymers include numerousthermoplastic and elastomeric polymeric materials that are known in theart. Polyolefins such as metallocene catalyzed polyethylenes,polypropylenes, and polybutylenes and copolymers thereof; ethylenicpolymers such as polystyrene; ethylenic copolymers such as ethylenevinyl acetate (EVA), ethylene-methacrylic acid and ethylene-acrylic acidcopolymers where some of the acid groups have been neutralized witheither zinc or sodium ions (commonly known as ionomers); polyacetals;chloropolymers such as polyvinylchloride (PVC); fluoropolymers such aspolytetrafluoroethylene (PTFE); polyesters such as polyethyleneterephthalate (PET); polyester-ethers; polysulfones; polyamides such asnylon 6 and nylon 6,6; polyamide ethers; polyethers; elastomers such aselastomeric polyurethanes and polyurethane copolymers; silicones;polycarbonates; and mixtures and block or random copolymers of any ofthe foregoing are non-limiting examples of biostable biocompatiblepolymers useful for manufacturing the medical devices of the presentinvention.

Additional exemplary biocompatible biostable polymers, which are notnecessarily exclusive of those listed in the prior paragraph, aredescribed in U.S. Pat. No. 6,153,252, the disclosure of which isincorporated by reference. These polymers include polyurethanes,silicones, poly(meth)acrylates, polyesters, polyalkylene oxides such aspolyethylene oxide, polyvinyl alcohols, polyethylene glycols andpolyvinyl pyrrolidone; hydrogels such as those formed from crosslinkedpolyvinyl pyrrolidone and polyesters could also be used. Other polymersinclude polyolefins, polyisobutylene and ethylene-alphaolefincopolymers; acrylic polymers (including methacrylic polymers) andcopolymers, vinyl halide polymers and copolymers, such as polyvinylchloride; polyvinyl ethers, such as polyvinyl methyl ether;polyvinylidene halides such as polyvinylidene fluoride andpolyvinylidene chloride; polyacrylonitrile, polyvinyl ketones; polyvinylaromatics such as polystyrene; polyvinyl esters such as polyvinylacetate; copolymers of vinyl monomers with each other and olefins, suchas ethylene-methyl methacrylate copolymers, acrylonitrile-styrenecopolymers, ABS resins and ethylene-vinyl acetate copolymers;polyamides, such as nylon 6,6 and polycaprolactam; alkyd resins;polycarbonates; polyoxymethylenes; polyimides; polyethers; epoxy resins;rayon; rayon-triacetate, cellulose, cellulose acetate, cellulose acetatebutyrate; cellophane; cellulose nitrate; cellulose propionate; celluloseethers (i.e. carboxymethyl cellulose and hydroxyalkyl celluloses); andcombinations thereof. Polyamides for the purpose of this applicationwould also include polyamides of the form —NH—(CH₂)_(n)—CO—andNH—(CH₂)_(x)—NH—CO—(CH₂)_(y)—CO, wherein n is typically an integer infrom 6 to 13; x is an integer in the range of form 6 to 12; and y is aninteger in the range of from 4 to 16. Mixtures and block or randomcopolymers of any of the foregoing are also useful in the presentinvention.

Among particularly beneficial biostable polymeric materials arepolyolefins, polyolefin-polyvinylaromatic copolymers includingpolystyrene-polyisobutylene copolymers and butadiene-styrene copolymers,ethylenic copolymers including ethylene vinyl acetate copolymers (EVA)and copolymers of ethylene with acrylic acid or methacrylic acid;elastomeric polyurethanes and polyurethane copolymers; metallocenecatalyzed polyethylene (mPE), mPE copolymers; ionomers;polyester-ethers; polyamide-ethers; silicones; and mixtures andcopolymers thereof.

Also among particularly beneficial biostable polymeric materials areblock copolymers having at least two polymeric blocks A and B. Examplesof such block copolymers include the following: (a) BA (linear diblock),(b) BAB or ABA (linear triblock), (c) B(AB)_(n) or A(BA)_(n) (linearalternating block), or (d) X-(AB)_(n) or X—(BA)_(n) (includes diblock,triblock and other radial block copolymers), where n is a positive wholenumber and X is an initiator molecule (also sometimes referred to as astarting seed molecule). One specific group of polymers have X-(AB)_(n)structures, which are frequently referred to as diblock copolymers andtriblock copolymers where n=1 and n=2, respectively (this terminologydisregards the presence of the initiator molecule, for example, treatingA-X-A as a single A block with the triblock therefore denoted as BAB).Where n=3 or more, these structures are commonly referred to asstar-shaped block copolymers.

The A blocks are typically soft elastomeric components which are basedupon one or more polyolefins, for example, a polyolefinic block havingalternating quaternary and secondary carbons of the general formulation:—(CRR′—CH₂)_(n)—, where R and R′ are linear or branched aliphatic groupssuch as substituted or unsubstituted methyl, ethyl, propyl, isopropyl,butyl, isobutyl and so forth, or substituted or unsubstituted cyclicaliphatic groups such as cyclohexane, cyclopentane, and the like.Specific examples include blocks of based on isobutylene,

(i.e., polymers where R and R′ are the same and are methyl groups) andblocks based on ethylene and butylene.

The B blocks are typically hard thermoplastic blocks that, when combinedwith the soft A blocks, are capable of, inter alia, altering oradjusting the hardness of the resulting copolymer to achieve a desiredcombination of qualities. Beneficial B blocks are polymers ofmethacrylates or polymers of vinyl aromatics. More beneficial B blocksare (a) made from monomers of styrene

styrene derivatives (e.g., α-methylstyrene, ring-alkylated styrenes orring-halogenated styrenes) or mixtures of the same or are (b) made frommonomers of methylmethacrylate, ethylmethacrylate hydroxyethylmethacrylate or mixtures of the same.

Typical initiator molecules are those known in the art and includetert-ester, tert-ether, tert-hydroxyl or tert-halogen containingcompounds, for example, cumyl esters of hydrocarbon acids, alkyl cumylethers, cumyl halides and cumyl hydroxyl compounds as well as hinderedversions of the above.

Particular polymers within this category include (a) copolymers ofpolyisobutylene with polystyrene or polymethylstyrene, for example,polystyrene-polyisobutylene-polystyrene (SIBS) triblock copolymers;these polymers are described, for example, in U.S. Pat. No. 5,741,331,U.S. Pat. No. 4,946,899 and United States Patent Application20020107330, each of which is hereby incorporated by reference in itsentirety; and (b) a copolymer containing one or more blocks ofpolystyrene and one or more random blocks of ethylene and butylene, forexample, a polystyrene-polyethylene/butylene-polystyrene (SEBS)copolymer, available as Kraton™ G series polymers available from KratonPolymers.

Typical biodisintegrable polymers include, but are not limited to,polylactic acid, polyglycolic acid and copolymers and mixtures thereofsuch as poly(L-lactide) (PLLA), poly(D,L-lactide), polyglycolic acid(polyglycolide), poly(L-lactide-co-D,L-lactide),poly(L-lactide-co-glycolide), poly(D, L-lactide-co-glycolide),poly(glycolide-co-trimethylene carbonate),poly(D,L-lactide-co-caprolactone), poly(glycolide-co-caprolactone),polyethylene oxide (PEO), polydioxanone, polypropylene fumarate,poly(ethyl glutamate-co-glutamic acid),poly(tert-butyloxy-carbonylmethyl glutamate), polycaprolactone,polycaprolactone co-butylacrylate, polyhydroxybutyrate and copolymers ofpolyhydroxybutyrate, poly(phosphazene), poly(phosphate ester),poly(amino acid) and poly(hydroxy butyrate), polydepsipeptides, maleicanhydride copolymers, polyphosphazenes, polyiminocarbonates, poly[(97.5%dimethyl-trimethylene carbonate)-co-(2.5% trimethylene carbonate)],cyanoacrylate, hydroxypropylmethylcellulose, polysaccharides such ashyaluronic acid, chitosan and regenerate cellulose, tyrosine-basedpolymers (e.g., tyrosine-derived polycarbonates such as the Tyrosorb™Synthetic Polymers available from Integra LifeSciences and thosedescribed in U.S. Pat. No. 6,120,491), and proteins such as gelatin andcollagen and genetically engineered variants thereof (e.g., collagenengineered to include thrombin cleavage sites), as well as mixtures andcopolymers of the above, among others.

Additional biodisintegrable polymers, which are not necessarilyexclusive of those listed in the prior paragraph, are described in U.S.Pat. No. 6,153,252, the disclosure of which is incorporated byreference. These polymers include aliphatic polyesters, poly(aminoacids), copoly(ether-esters), polyalkylene oxalates, polyamides,poly(iminocarbonates), polyorthoesters, polyoxaesters, polyamidoesters,polyoxaesters containing amido groups, poly(anhydrides),polyphosphazenes, biomolecules, and blends thereof. For the purpose ofthis invention, aliphatic polyesters include homopolymers and copolymersof lactide (which includes lactic acid d-,l- and meso lactide),epsilon-caprolactone, glycolide (including glycolic acid),hydroxybutyrate, hydroxyvalerate, para-dioxanone, trimethylene carbonate(and its alkyl derivatives), 1,4-dioxepan-2-one, 1,5-dioxepan-2-one,6,6-dimethyl-1,4-dioxan-2-one and polymer blends thereof. Amongpoly(iminocarbonate)s useful in the present invention include thosedescribed by Kemnitzer and Kohn, in the Handbook of BiodegradablePolymers, edited by Domb, Kost and Wisemen, Hardwood Academic Press,1997, pages 251-272. Among copoly(ether-esters) useful in the presentinvention include those copolyester-ethers described in Journal ofBiomaterials Research, Vol. 22, pages 993-1009, 1988 by Cohn and Younesand Cohn, Polymer Preprints (ACS Division of Polymer Chemistry) Vol.30(1), page 498, 1989 (e.g. PEO/PLA). Among polyalkylene oxalates usefulin the present invention include those described in U.S. Pat. Nos.4,208,511; 4,141,087; 4,130,639; 4,140,678; 4,105,034; and 4,205,399(incorporated by reference herein). Among polyphosphazenes, co-, ter-and higher order mixed monomer based polymers made from L-lactide,D,L-lactide, lactic acid, glycolide, glycolic acid, para-dioxanone,trimethylene carbonate and epsilon-caprolactone useful in the presentinvention include those described by Allcock in The Encyclopedia ofPolymer Science, Vol. 13, pages 31-41, Wiley Intersciences, John Wiley &Sons, 1988 and by Vandorpe, Schacht, Dejardin and Lemmouchi in theHandbook of Biodegradable Polymers, edited by Domb, Kost and Wisemen,Hardwood Academic Press, 1997, pages 161-182 (which are herebyincorporated by reference herein). Polyanhydrides from diacids of theform HOOC—C₆H₄—O—(CH₂)_(m)—O—C₆H₄—COOH where m is an integer in therange of from 2 to 8 and copolymers thereof with aliphatic alpha-omegadiacids of up to 12 carbons are also useful in the present invention.Among polyoxaesters, polyoxaamides and polyoxaesters containing aminesand/or amido groups useful in the present invention include thosedescribed in one or more of the following U.S. Pat. Nos. 5,464,929;5,595,751; 5,597,579; 5,607,687; 5,618,552; 5,620,698; 5,645,850;5,648,088; 5,698,213 and 5,700,583 (which are incorporated herein byreference). Polyorthoesters include those described by Heller inHandbook of Biodegradable Polymers, edited by Domb, Kost and Wisemen,Hardwood Academic Press, 1997, pages 99-118 (hereby incorporated hereinby reference). Biodisintegrable polymers also include naturallyoccurring materials that may be enzymatically degraded in the human bodyor are hydrolytically unstable in the human body such as fibrin,fibrinogen, collagen, elastin, and absorbable biocompatiblepolysaccharides such as chitosan, starch, fatty acids (and estersthereof), glucoso-glycans and hyaluronic acid. Mixtures and block orrandom copolymers of any of the foregoing are also contemplated.

A layer of the polymer can be provided upon the medical device usingessentially any technique known in the art. For example, where thepolymer can be applied as a liquid (e.g., where monomer is applied as aliquid and subsequently polymerized; where the polymer is dissolved ordispersed in a solvent or carrier liquid and the solvent or carrierliquid subsequently removed; or, where the polymer is a thermoplasticmaterial that can be heated to above its melting point, applied andsubsequently cooled), a number of techniques are available forapplication, including casting, spin coating, web coating, spraycoating, dip coating, fluidized bed coating, positive displacementcoating, ink jet techniques and so forth. Where the polymer is of athermoplastic character, a variety of additional standard thermoplasticprocessing techniques can also be used including compression molding,injection molding, blow molding, spinning, vacuum forming andcalendaring, as well as extrusion.

In general, it is desirable to control the release of the therapeuticagent from the medical device such that therapeutic agent remainsavailable for release after the device is fully deployed at thetreatment site. This typically means that no more than about 50%, andmore typically no more than about 10%, of the therapeutic agent isreleased prior to full deployment of the medical device.

For restenosis treatment, it is desirable that the release be initiatedbefore or at the time at which cell proliferation occurs, whichgenerally begins approximately three days after the injury to the arterywall by the PTCA procedure. Of course, the release profile will betailored to the condition that is being treated. For example, where ananti-inflammatory or anti-thrombotic effect is desired, release istypically initiated sooner. Moreover, in instances where DNA is usedthat has an expression half-life that is shorter than the time perioddesired for administration of the therapy, release of the DNA from thedevice is typically regulated such that it occurs over a time periodlonger than the half-life of the DNA expression, thus allowing newcopies of DNA to be introduced over time and thereby extending the timeof gene expression.

The performance of the medical devices of the invention can be evaluatedin vitro in a number of ways, including investigation of the releasekinetics of the therapeutic agent, as well as the integrity of thetherapeutic agent that is released. For instance, in the case where thetherapeutic agent is a high-molecular-weight therapeutic agent such asDNA, the conformational and structural integrity of the DNA can beinvestigated.

In many embodiments of the invention, high-molecular-weight therapeuticagents are incorporated during the processing of the polymer materialthat forms a coating on a surface of the medical device. However, thetherapeutic agents may not be stable under the conditions required forsuch processing. For instance, high-molecular-weight therapeutic agentssuch as polynucleotides and polypeptides, and especially polynucleotidesin the form of plasmid DNA, may be subjected to substantial shearstresses when they are mixed with a polymer and applied to a medicaldevice as described above. This is especially true where an organicsolvent is used to process the polymer. In these cases, polynucleotidessuch as plasmid DNA are commonly insoluble in these organic solvents.Although water/oil emulsions can be prepared to facilitate dispersion ofthe plasmid DNA, the use of high speed mechanical mixing to achieveeffective emulsification can result in shearing of the polynucleotide,ultimately reducing transfection efficiency.

In accordance with certain embodiments of the present invention, thisobstacle is addressed by first precipitating or depositing thepolynucleotide (or other high-molecular-weight therapeutic agent) on thesurface of the medical device. Subsequently, a polymeric barrier layeris provided over the polynucleotide layer. In this way, shear stressesupon the polynucleotide can be controlled, and the release of thepolynucleotide can be regulated. The rate of release of the activepolynucleotide can be controlled by the type and construction of thepolymeric barrier layer. At the same time, the polynucleotide isprotected by the polymer from rapid degradation within the patient.

Various methods are available for forming a precipitated layer ofpolynucleotide upon the medical device. For example, a solution of thepolynucleotide can first be provided. Then, the medical article can bedipped into the polynucleotide solution, followed by drying.Alternatively, the polynucleotide solution can be applied to the medicalarticle by other coating techniques such as those previously discussed(e.g., solvent casting, spin coating, web coating, spray coating,fluidized bed coating, positive displacement coating, and ink jettechniques), so long as the shear stresses are kept to tolerable levels.Dipping the medical device in an aqueous solution of polynucleotide isan example of a method of forming the precipitated layer.

The precipitated layer of polynucleotide is subsequently covered with alayer of polymer, such as those discussed above, which acts as a barrierfor the release of the polynucleotide. The polymer layer can be appliedusing any of the coating techniques previously discussed and can eitherbe biostable, in which case the polynucleotide will be transportedthrough the layer, or biodisintegrable, in which case the polynucleotideis released by transport through the layer, by disintegration (e.g.,biodegradation, bioerosion and/or dissolution) of the layer, or both.

Regardless of whether the therapeutic agent is disposed within thepolymer or whether the polymer acts as a barrier layer, it may bedifficult in some instances to achieve adequate transport of thetherapeutic agent through the polymer to effect significant release,especially where the therapeutic agent is a high-molecular-weighttherapeutic agent. For example, this difficulty is observed on occasionfor various biostable polymers, including block copolymers comprisingpolymer blocks of olefin molecules and polymer blocks of vinyl aromaticmolecules, for example, block copolymers of polyisobutylene andpolystyrene (or of polyisobutylene and polystyrene derivatives such aspoly α-methylstyrene).

In certain embodiments of the present invention, these transport issuesare addressed by combining the polymer with a removable material.Without wishing to be bound by theory, it is believed that, by providinga removable material according to the above embodiments of theinvention, a more porous polymer is provided, increasing the transportof high-molecular-weight therapeutic agent through the polymer.

In some embodiments, the removable materials are leachable materials(i.e., materials that can be extracted by exposure to a solvent or otheragent that causes removal of the leachable material). In theseembodiments, the leachable material and the polymer are combined andassociated with the medical device, typically by applying thecombination to the medical device surface. Subsequently, the leachablematerial is removed either in vitro (i.e., before insertion orimplantation) or in vivo (i.e., after insertion or implantation). Wherethe leachable material is removed in vitro, the solvent may be selectedsuch that the leachable material is removed from the polymer, while thehigh-molecular-weight therapeutic agent that is present is notsubstantially removed (for example, in the case where DNA is selected asthe therapeutic agent, a leachable material can be selected that isremovable upon solvent exposure, while the DNA remains undissolved inthe solvent). The leachable material can be removed in vivo for example,upon exposure of the leachable material to a physiological fluid, whichdissolves, erodes or degrades the leachable material.

For example, the polymer may comprise a biostable polymer having regionsof leachable material dispersed therein. The leachable material can beremoved from the remaining bulk of biostable polymer by mechanisms suchas dissolution, erosion or degradation. It is also effective to utilizea biodisintegrable polymer having leachable regions dispersed therein,so long as the time frame within which the leachable regions are removedis substantially shorter than the time frame within which the remainingbulk of the polymer disintegrates. These regions will, therefore,degrade more quickly, providing, as discussed below, means to increasetransport of the high-molecular-weight therapeutic agent through theremaining biodisintegrable polymer.

Typical leachable materials include the following: polyethylene glycol(also known as polyoxyethylene), polyalkylene oxides includingpolyethylene oxide and polyethylene oxide/polypropylene oxide copolymers(also known as poloxamers), polyhydroxyethylmethacrylate,polyvinylpyrrolidone, polyacrylamide and its copolymers, polylactides,polyglycolides, polyanhydrides, polyorthoesters and their copolymers,proteins including albumin, peptides, liposomes, cationic lipids, ionicor nonionic detergents, salts including potassium chloride, sodiumchloride and calcium chloride, sugars including galactose, glucose andsucrose, polysaccharides including soluble celluloses, heparin,cyclodextrins and dextran, and blends of the same. Further leachablematerials can be found among the biodisintegrable polymers listed above.

Where a polynucleotide is used as the high-molecular-weight therapeuticagent, leachable components that are further known to improvetransfection efficacy, such as polyalkylene oxides, cationic lipids,liposomes and cyclodextrins, are particularly beneficial.

Moreover where the polymer that is selected contains hydrophobicelements, for example, biostable copolymers having blocks ofpolyisobutylene and polystyrene, the leachable component is ideallyamphiphilic to assist with the formulation of the polymer (e.g., wherean water-in-oil or oil-in-water emulsion is formed during formulation).Typical amphiphilic leachable components include polyalkylene oxides andionic or nonionic detergents.

Thus, leachable components such as polyalkylene oxides are particularlybeneficial for the practice of the invention, because they can (1) likeother leachable components, enhance therapeutic agent transport upondeployment of the medical device, (2) provide stable emulsions due totheir amphiphilic properties, particularly during matrix formation withpolymers containing hydrophobic elements, and (3) enhance cellularuptake of polynucleotides due to their transfection-enhancingcharacteristics.

In other embodiments, the removable materials are evaporable. In some ofthese embodiments, the evaporable materials may comprise evaporablesalts such as ammonium salts (e.g., ammonium bicarbonate).Alternatively, they may comprise the oil phase and/or the water phase ina water-in-oil or oil-in-water emulsion of the polymer and thehigh-molecular-weight therapeutic agent. Typical emulsifying agents forthis purpose include polyalkylene oxides and detergents. Typical oilphase materials include toluene, tetrahydrofuran, butyl acetate,chloroform, and methylene chloride. In this embodiment, the emulsion istypically applied to a surface of the medical device, after which thevolatile or evaporable phases (typically the water and oil) are removed,for example, by applying heat under vacuum conditions. It is also notedthat, in many instances, the emulsifying agent will also elute from thepolymer once the medical device is inserted or implanted as discussedabove, removing further material from the polymer. Moreover, where apolynucleotide is used as the high-molecular-weight therapeutic agent,emulsifying agents that are also known to improve transfection efficacy,such as polyalkylene oxides and cationic lipids, are particularlybeneficial.

In general, it is desirable to tailor the release profile of therapeuticagent from the medical devices of the present invention. According tocertain embodiments of the invention, release can be tailored byproviding a medical device that has a multi-layer coating covering atleast a portion of the medical device. The multi-layer coating includes:(a) one or more therapeutic agent containing layers and (b) one or morepolymeric layers. The one or more polymeric layers provide a polymercomposition gradient in a direction normal to the surface of the coating(i.e., a gradient in the polymer composition is observed as one proceedsdeeper into the coating). Although these embodiments may be used withall sizes of therapeutic agents, high-molecular-weight therapeuticagents are particularly beneficial.

Such a polymer composition gradient can be provided in a number of ways.As an example, a single polymeric layer can be provided, which has acomposition gradient over its thickness. As another example, multiplepolymeric layers of differing composition can be disposed over oneanother to collectively provide a polymer composition gradient in adirection normal to the surface of the coating.

In some embodiments, the therapeutic agent containing layers aredisposed beneath the polymeric layers. In other embodiments, thetherapeutic agent containing layers are interspersed between thepolymeric layers, typically in an alternating configuration. In eithercase, the therapeutic agent release profile that is associated with themedical device is shaped by the composition gradient that is establishedwithin the polymeric portion of the multi-layer coating. Moreover, thetherapeutic agent release profile can be tuned by varying the shape ofthis gradient.

One way to establish a polymer layer composition gradient is to vary thecomposition of the polymer material itself. For example, the relativeamounts of two or more monomers within a copolymer can be varied toestablish such a gradient. Alternatively, the relative amounts of two ormore polymers (including copolymers) within a polymer blend can bevaried.

As a specific example, the relative amounts of a hydrophobic polymer(for example, a polystyrene-polyisobutylene copolymer such as thepolystyrene-polyisobutylene-polystyrene block copolymers discussedabove) and a hydrophilic polymer (for example, a styrene-ethyleneoxidecopolymer such as a polystyrene-polyethylene oxide-polystyrene triblockcopolymer) can be varied within a polymer blend to create ahydrophobicity gradient within the coating.

As a more specific example, a layer containing a hydrophilic therapeuticagent such as plasmid DNA is deposited on a medical device such as astent. Subsequently, multiple layers, each containing a blend ofhydrophilic and hydrophobic polymers, are deposited over the therapeuticagent-containing layer. The innermost deposited layer is provided withthe greatest relative amount of hydrophobic polymer, with eachsubsequently deposited layer containing higher and higher relativeamounts of hydrophilic polymer. As a result, a hydrophobicity gradientis established.

Conversely, with a hydrophobic therapeutic agent such as paclitaxel, theinnermost layer is provided with the greatest relative amount ofhydrophilic polymer, with subsequent layers containing relativelygreater amounts of hydrophobic polymer.

Another way to establish a polymer layer composition gradient is to varythe porosity within the polymer layers. Polymer porosity can beestablished, for example, during the course of polymer formation orsubsequent to polymer formation. For example, polymer porosity can beestablished by providing the polymer with a removable component, such asthose discussed above. Upon removal of the removable component (e.g.,either in vitro or in vivo), a porous structure is established. (Asdiscussed further below, where the leachable component is dissolved uponimplantation or insertion of the medical device in vivo, an osmoticgradient is also established, which can also influence therapeutic agentrelease.)

Another way to establish a polymer layer composition gradient is to varythe concentration of one or more additional species the polymer layers.For example, by varying the concentration of an acidic or basic specieswithin the one or more polymer layers, a pH gradient can be provided.Examples of basic and acidic species include polylysine polymers andpolyacrylic acids (e.g., carbopol).

As another example, an osmotic gradient can be provided by varying theconcentration of a soluble species within the one or more polymerlayers. Examples of soluble species include the soluble leachablespecies listed above.

As another example, a charge gradient can be provided by varying theconcentration of an ionic species within the one or more polymer layers.Examples of ionic species for this purpose include potassiummetaphosphates.

In many embodiments of the present invention, it is desirable to apply apolymer to an expandable medical device, such as a stent or a ballooncatheter, for example, by providing a coating of the polymer on thedevice. This can occur, for example, in the case where ahigh-molecular-weight therapeutic agent is disposed within the polymer(i.e., within a polymer matrix) or where the polymer acts as a barrierlayer for a high-molecular-weight therapeutic agent. With many polymermaterials, however, polymer cracking can occur upon expansion of themedical device. Moreover, where large amounts of polymer coating areused (e.g., in response to the need for large amounts of therapeuticagent), cracking difficulties upon implantation or insertion of themedical device can be exacerbated.

To address such issues, the polymer in some embodiments of the inventionis admixed with a plasticizer to improve the polymer's resistance tocracking, thus avoiding, for example, uncontrolled release, embolismrisks and unsuccessful therapeutic outcomes.

The plasticizer can also be selected to modify the rate at which thehigh-molecular-weight therapeutic agent is released from the polymer,for example, by influencing the diffusivity of the high-molecular-weighttherapeutic agent within the polymer or by influencing the degradationrate of a biodisintegrable polymer.

Typical plasticizers include for example: glycerol (glycerin USP),triacetyl glycerin (triacetin), ethylene glycol, triethylene glycol,polyethylene glycol, propylene glycol, polyalkylene oxides includingpolyethylene oxide and polyethylene oxide/polypropylene oxidecopolymers, citric acid esters, sebacic acid esters, phthalic acidesters, silicone fluids, and analogs and derivatives and mixturesthereof.

In some embodiments, the plasticizer functions both to provideresistance to cracking of the polymer and as a leachable material, whichas discussed above is believed to provide a more porous polymer network,facilitating transfer of the high-molecular-weight therapeutic agentthrough the polymer. Examples of plasticizers that provide this dualfunctionality include, but are not limited to, ethylene glycol,triethylene glycol, polyethylene glycol, propylene glycol, polyalkyleneoxides including polyethylene oxide and polyethylene oxide/polypropyleneoxide copolymers.

Where a polynucleotide is used as the high-molecular-weight therapeuticagent, plasticizers that are also known to improve transfectionefficacy, such as polyalkylene oxides and cationic lipids, areparticularly beneficial.

EXAMPLES Example 1 Materials

Biodisintegrable polymers: (a) poly(lactic-co-glycolic acid) (50 mol %lactic acid-50 mol % glycolic acid) having acid end groups availablefrom MediSorb, hereinafter referred to as “PLGA (acid end groups”), (b)low molecular weight poly(lactic-co-glycolic acid) (50 mol % lacticacid-50 mol % glycolic acid) available from MediSorb, hereinafterreferred to as “PLGA (low molecular weight), (c) collagen type I(available from Sigma), (d) gelatin type A (available from Sigma), (e)gelatin type B (available from Sigma), and (f) hyaluronic acid(available from Anika Therapeutics) (HA).

Plasticizers: (a) triacetin (Sigma), (b) sebacic acid dibutyl ester(Sigma), (c) glycerol (Sigma), (d) polyethylene glycol 3350 (PEG) (UnionCarbide) and (f) silicon oil (Dow Corning).

A 4-kilobase reporter plasmid pNGVL2 (University of Michigan) encodingbeta-galactosidase was isolated by cationic affinity chromatography andpurified by CsCl gradient centrifugation for use herein.

Example 2 Stent Coating

PLGA (low molecular weight) and PLGA (acid end groups) were homogenized(2 minutes, highest level) separately into a stable emulsion withplasmid DNA (18.6 mg/ml) in a (3:1) (mg:ul) ratio. NIR stents (7/9 mm)were dipped into the two different solutions for 15 seconds and thenspun to remove excess coating from the windows of the stent. The coatedstents were then dried in a vacuum oven at 40° C. overnight beforetesting.

Collagen was formulated with poly(acrylic acid) (PAA) (available fromAldrich) as a model for DNA (10 mg/ml) in a (5:1) (mg:mg) ratio andsprayed onto the stent. The spraying parameters were then adjusted toproduce the optimal level of coating.

Stents were coated with both types of gelatin in the same procedure ascollagen. In addition, the glycerol and PEG plasticizers were used inthe formulation at different concentrations (5 to 30 wt/o for the PEGand 12.5 to 25 wt % for the glycerol) to help prevent cracking.

Stents were coated with hyaluronic acid in the same procedure ascollagen. The plasticizers PEG, triacetin, sebacic acid dibutyl ester,and polyethylene glycol 3350 (PEG) were used in the formulation todetermine their effect on cracking, and the formulation with the bestproperties was used to encapsulate DNA. For example, 22 wt % silicon oil(Si) and 78 wt % hyaluronic acid (HA) are first homogenized for fiveminutes into a stable emulsion. An Si-HA:DNA emulsion is then made byadding DNA (typically 18.6 mg/ml) in a (1:1) (mg:ul) ratio homogenizingfor two additional minutes. Stents were dipped for 10 seconds and spunat a high rpm to remove excess coating. (1:1) (mg:ul) HA:DNA sampleswere also made by homogenizing for two minutes at the highest level andthen following the same dipping and spinning procedure as above.

Example 3 Conformational Analysis of Released DNA

Released DNA was assessed through 1% agarose gel electrophoresis (70 V,1 h) in the presence of ethidium bromide and compared to un-encapsulatedplasmid DNA to determine the structural integrity and purity of releasedDNA.

Example 4 Analysis of Coating Solubility and DNA release

The various coatings were evaluated for solubility by dipping the coatedstents in PBS with a pH of 7.4 for predetermined intervals, and bymeasuring the amount of coating dissolved during each time span.Similarly, in vitro release of plasmid DNA was evaluated for each stentby immersing the stent in PBS of 7.4 pH, and by measuring theconcentration of released plasmid DNA in the solution at 280 nm.

Example 5 Evaluation of Coating Mechanical Integrity

The mechanical integrity of the coatings was evaluated by viewing thestents under an optical microscope to determine the extent of webbingover windows of the stent, and by viewing the coating under a scanningelectron microscope (SEM) to determine cracking and surfacecharacteristics of the polymer before and after expansion of the stent.

Example 6 Mechanical Integrity of Coating, DNA Release and DNA IntegrityAssociated with PLGA Polymers

Table 1 shows the ratio PLGA to DNA for several stent samples. Table 1also shows the average coating weight for the coating of the polymer ona stent, which is representative of the thickness of the coating, andindicates whether the coating cracked or not when the stent wasexpanded.

Under optical microscopy, stents coated from both types of PLGA wereshown to exhibit webbing and filled windows. However, PLGA (acid endgroups) has approximately twice the amount of coating by weight on thestent than PLGA (low molecular weight) as seen from Table 1 below. Whenanalyzed by SEM, PLGA (acid end groups) did not crack upon expansion ofthe stent even when the windows were filled with the polymer. However,PLGA (low molecular weight) does exhibit cracking upon expansion of thestent when analyzed by SEM.

TABLE 1 Characteristics of PLGA Ave. PLGA:DNA Coating # of Ratio WeightSamples Cracking PLGA (low molecular (3:1) 2500 μg 3 Yes weight) PLGA(acid end groups) (3:1) 4700 μg 3 No PLGA (acid end groups) (1:1) 3500μg 3 No

DNA release curves were generated from the release kinetics of DNA fromstents coated with both types of PLGA (presented in FIGS. 4 and 5 withtwo different time scales). The percent cumulative release of PLGA (acidend groups) was significantly higher than PLGA (low molecular weight) atall time points. More than 25% of the plasmid DNA within the PLGA (acidends groups) was released within 20 days, while PLGA (low molecularweight) only released 12% within that same time period. Both types ofPLGA show a burst of release of DNA within the first two hours. 1 μg

Contrary to what was expected, the percent cumulative release rate of(3:1) PLGA:DNA coated samples was higher than the (1:1) PLGA:DNA coatedsamples (FIG. 5). This could be due to the initial burst of DNA releasewithin the first few minutes for the (3:1) PLGA:DNA samples. Also, theamount of coating achieved on the stents was less for the (1:1) samplesthan the (3:1) samples, as there was less plugging of the windows of thestent. SEM pictures of released stents show that most of the PLGAcoating has been removed from the stent after approximately 70 days, andonly some residual coating remains.

Plasmid DNA released from both types of PLGA was analyzed to determinethe conformation of the DNA. The control plasmid DNA was primarily insupercoiled form (4 kb band) while the released PLGA/DNA showsconversion to the open circular form (6 kb band). The bands formed fromthe PLGA/DNA samples are low in intensity.

Example 7 Mechanical Integrity of Coating, DNA Release and DNA IntegrityAssociated with Gelatin, Collagen and Hyaluronic Acid Polymers

A summary of the characteristics for the additional biodisintegrablepolymers is shown in Table 2. Table 2 indicates the average coatingweight for various combinations, whether the coating cracked uponexpansion of the stent, and the average dissolution rate for certain ofthe combinations.

TABLE 2 Characteristics of Additional Polymers Ave. Ave. CoatingDissolution Polymer Weight Cracking Rate Hyaluronic Acid (HA) 300 μg Yes 8 μg/min Gelatin Type B 500 μg Yes 43 μg/min Gelatin Type A 350 μg Yes44 μg/min Collagen Type I 650 μg Yes 43 μg/min Gel B w/ 12.5% Glycerol2000 μg  No Gel B w/ 22% Glycerol 700 μg No HA w/ 5% PEG 1000 μg  SomeHA w/ 10% PEG 1600 μg  Some HA w/ 10% Si 450 μg No HA w/ 22% Si 700 μgNo HA w/ 30% Si 700 μg No Si-HA:DNA 1300 μg  No HA-DNA 150 μg Yes

A significant amount of collagen coating was achieved upon thestent-typically greater than the amount of coatings for the otherpolymers without plasticizer. Collagen was found to have a highsolubility, and initial formulations of collagen with PAA resulted inthe precipitation of PAA. Stents coated with this polymer also exhibitedextensive cracking upon expansion.

Both types of gelatin exhibited moderately high solubility, a highinitial degradation rate and cracking upon expansion of the stent. PAAwas also shown to precipitate readily from formulations with gelatintype A.

Incorporation of glycerol as a plasticizer into both types of gelatinresulted in the elimination of cracking of the polymer coating, as seenfrom SEM photographs and also resulted in a 400% increase in the amountof coating on the stent. With this addition, some increase in thesolubility of gelatin in PBS can be seen (FIG. 6). There is a initialburst of dissolution within the first 1½ minutes, where at least 80% ofthe coating with the addition of glycerol is dissolved, as opposed tojust 60% of pure gelatin type B, making glycerol an unattractiveplasticizer for certain longer-term applications.

PEG was found to separate out of solution when combined with gelatin,and was not pursued further.

Turning now to hyaluronic acid, the generated solubility curves of FIG.7 indicate that hyaluronic acid coatings have a lower solubility thancoatings of both types of gelatin and collagen.

Studies of hyaluronic acid with the plasticizers triacetin and sebacicacid dibutyl ester showed that, even if the solution is homogenized intoan emulsion, the plasticizers separate out of solution within one-halfhour. The plasticizer PEG was found to be stable in solution however,and to greatly reduce the amount of cracking of the polymer coated stentwhen viewed by SEM, as well as increase the amount of coating on thestent by up to 500% (see Table 2). Incorporation of silicon oil (Si)into the hyaluronic acid plasticizer helped to eliminate cracking of thepolymer-coated stent when viewed by SEM, and to increase the amount ofcoating achieved upon the stent by over 200% (Table 2).

Solubility tests PBS indicate that PEG, presumably because it is ahydrophilic compound, increases the solubility of hyaluronic acid. FIG.8 shows that there is a 95% initial burst phase of dissolution withinthe first five minutes where PEG is used. Almost all of the PEG/HAcoating is dissolved within the first four minutes as compared to only35% of a pure hyaluronic acid sample. On the other hand, solubilitytests of hyaluronic acid and silicon oil show that the incorporation ofsilicon lowers the solubility of hyaluronic acid. There is a directcorrelation between the increase in concentration of silicon oil anddecrease in solubility of hyaluronic acid.

Only approximately 150 μg of coating was achieved on the HA/DNA coatedstents, while the Si-HA/DNA samples had an average of 1300 μg (Table 2).SEM photographs show a uniform coating for both types of DNA containingpolymers upon the stent. It was also found that essentially no crackingoccurs upon expansion of stents coated with Si-HA/DNA, while stentscoated with HA/DNA show cracking both before and after (to a greaterextent) expansion.

DNA release curves (FIG. 9) of hyaluronic acid show that most of theDNA, over 25 μg, is released within 20 minutes. The Si-HA samples show a30 μg cumulative release during the first 45 minutes, followed by agradual elution of up to 46 μg cumulative release over a period of 1½days. In terms of DNA release in percentages, both HA and Si-HA samplesrelease up to approximately 35%, but the HA samples release this amounttwenty-three times faster than the Si-HA samples, with more than 22%released within the first five minutes (FIG. 10). SEM analysis and themass weight of released samples indicate that some coating remains onthe Si-HA stent even after the stent stops releasing DNA.

Hence, coatings for a stent containing HA (which is a biocompatible,non-toxic polymer) can be used to release plasmid DNA in a controlledand sustained manner. Since the coating fully dissolves within a fewdays, no residual coating is left on the stent after delivery of theplasmid DNA. As shown in FIG. 9, coatings containing silicon, HA and DNArelease the bulk of DNA between five minutes to an hour and a half afterinsertion. The silicon and HA polymer coating also allows a largeincrease in the amount of coating on the stent, without clogging of thestent windows or cracking of the polymer film.

The DNA samples released from the HA and Si-HA coated stents show twobands, possibly three, of unequal intensity upon the gel. For the Si-HAsamples, the lower band corresponds to the original pure supercoiledform of DNA (4 kb), while the more intense band (6 kb) corresponds tothe nicked, open circular form of DNA, suggesting that the majority ofthe DNA is in the nicked, open circular form. A possible, very faintthird band also seems to be apparent on the gel that could represent thelinear, degraded form of DNA. The presence of the less desirable opencircular form of the DNA is apparently due to homogenization of themixture, during which the large plasmid molecules is mechanicallysheared into the smaller molecules.

The HA-DNA samples show two bands of equal intensity corresponding tothe supercoiled and open circular form of DNA, suggesting a roughlyequal concentration of both forms. Similarly, a third band correspondingto the linear form of DNA might be represented on the gel. In both typesof HA samples, intensity of the band corresponds positively to theconcentration of DNA present in the released samples.

Example 8 Precipitation of DNA onto a Stent

For this example, stents were immersed in vials of DNA solutions (0.04to 4.9 mg DNA/ml deionized water) and stored at −20° C. overnight. Thevials were slowly brought to room temperature and stents were removed.Stents were placed on the mandrels and dried for 1 hour at 37° C.

From FIG. 11, it is seen that by increasing the concentration of DNA inthe starting solution, the amount of DNA that is adsorbed to the stentlikewise increases in a predictable manner.

Example 9 Polymer Overcoats

DNA coatings were prepared as described above in Example 8 (4.8 mg/mlDNA solution was used for this procedure). DNA films covered the stentwindows and remained intact after coverage with the overcoats. A 1%solution of PEG-PLGA (1000 molecular weight PEG; 70 mol % lactic acid-30mol % glycolic acid; inherent viscosity 0.45) in chloroform was sprayedover the DNA undercoat.

Upon examination under SEM, it was apparent that the stents with blockcopolymer overcoats of polyethylene glycol 1000/70:30 poly(DL-lactide-co-glycolide) (PEG-PLGA) became porous upon stent expansion.It is believed that the resulting porosity may enhance DNA diffusion,while also ensuring side branches of the vasculature do not becomeblocked. FIG. 12 graphically illustrates the release profile of DNA fromPEG-PLGA coated stents at various DNA and polymer overcoat loadings. Ascan be seen from this figure, the PEG/PLA overcoats modulated DNArelease. Increasing coating weights of PEG-PLGA were shown to decreaseDNA release.

FIG. 13 is a photograph of a stent after seven days of implantation in arabbit iliac artery. The stent was coated with plasmid DNA (containing aLacZ reporter gene) and subsequently provided with an overcoat ofpolyethylene glycol 1000/70:30 PEG-PLGA using procedures like thosedescribed above. β-galactosidase expression was used to assesstransduction. Photographed from the adventitial surface, the darkstaining observed around the stent struts in FIG. 13 is considered areasof cell transduction.

FIG. 14 graphically illustrates the release profile of DNA overcoatedwith a polystyrene-polyisobutylene-polystyrene triblock copolymer (SIBS)using procedures like those described above. The SIBS is produced usingprocedures like those described in U.S. Pat. No. 4,946,899 and UnitedStates Patent Application 20020107330. Incremental DNA release wasobserved over period of about 20 minutes. Although not illustrated,increasing coating weights of SIBS was shown to decrease DNA release.

Example 10 Addition of Polyethylene Glycol to Modulate Release ofDextran from a Polystyrene-Polyisobutylene-Polystyrene TriblockCopolymer Matrix

To determine the effect of PEG molecular weight on FITC-dextran(fluorescein-isothiocyanate-dextran, MW 70,000, available from Sigma)elution from a SIBS coating, three formulations were studied, as seen inFIG. 15. Formulations included 4.9% SIBS with 0.1% PEG (either 900,000MW, 100,000 MW, or 8,000 MW available from Polysciences) prepared with10% FITC-dextran (based on the weight of the SIBS/PEG solids). Thesuspension was pipetted onto coupons and dried at room temperature for 3hours. Coated coupons were immersed in PBS at 37° C. and releaseprofiles were obtained using spectrofluorometric detection of therelease of FITC-dextran. The amount of FITC-dextran released was derivedfrom a calibration curve plotted with known concentrations ofFITC-dextran.

FIG. 15 illustrates cumulative dextran release from a SIBS polymermatrix as a function of time for PEG of various molecular weights (i.e.,8,000, 100,000 and 900,000). As can be seen from this Figure, dextranrelease was substantially limited with the lower molecular weight PEGs(i.e., the 8,000 and 100,000 molecular weight PEGs), but not for thehigher molecular weight PEG (i.e., the 900,000 molecular weight PEG).

The methods associated with FIG. 15 were also used in connection withFIG. 16. In this case, FITC-dextran release was assessed as a functionof the amount of PEG 900,000 MW used. The addition of SIBS was varied toachieve an overall solids content of 5%.

FIG. 16 illustrates cumulative dextran release as a function of time forvarious ratios of SIBS and PEG900K (i.e., 900,000 molecular weight PEG)within the SIBS polymer matrix. As can be seen from FIG. 16, The 2.5%SIBS/2.5% PEG900K formulations shows a large burst of release over arelatively short time period, whereas the 4.99% SIBS/0.01% PEG900Kdemonstrated much lower release over an extended time period.

Example 11 Addition of Micronized Sodium Chloride to Increase Porosityof a Polystyrene-Polyisobutylene-Polystyrene Triblock Copolymer Matrix

A SIBS/NaCl suspension in chloroform was prepared (using 16% SIBS, 84%micronized NaCl) and immersed in a sonicator at maximum power for 5minutes to facilitate dispersion. Coupons were dipped in the dispersionand dried at 70° C. under vacuum for 2 hours. The salt was thenextracted from the coating by immersing the coupon in PBS for 22 hrs.

FIG. 17 is a micrograph of the 16% SIBS/84% micronized NaCl coatingfollowing 22 hours of extraction in PBS. The interconnected poresaveraged 7 um in diameter.

Example 12 Addition of DNA and Poloxamer to aPolystyrene-Polyisobutylene-Polystyrene Triblock Copolymer Matrix

9000 ppm of poloxamer (P104) available from BASF was used to stabilize awater-in-oil emulsion. The coating formulation was prepared by mixing9000 ppm P104 in toluene with SIBS. DNA (20 mg/ml stock solution) wasadded dropwise to a final organic:aqueous ratio of 3:1 (finalformulation: 9000 ppm P104, 7.5% SIBS and 0.5% DNA). Stents were dippedinto the emulsion and spun at 5000 rpm for 16 seconds. Samples weredried at 50° C. for 1 hour.

The use of 9000 ppm of poloxamer allowed a stable water-in-oil emulsionto be readily created with minimal mechanical mixing. In addition toassisting with emulsion formation, the use of the poloxamer furtherassisted in the formation of a porous polymer network. Moreover, asnoted above, literature studies have demonstrated enhanced DNAtransfection in the presence of poloxamers.

FIG. 18 is a graph of percent cumulative release as a function of timefor a stent coated with a matrix of SIBS, DNA and poloxamer. As can beseen from this figure, 50% of the DNA release occurred between 0 and 20minutes.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the structure and themethodology of the present invention, without departing from the spiritor scope of the invention, thus it is intended that the presentinvention covers the modifications and variations of this inventionprovided they come within the scope of the appended claims and theirequivalents.

1. A medical device, at least a portion of which is insertable orimplantable into the body of a patient, said medical device comprising:a therapeutic agent containing layer comprising a high-molecular-weighttherapeutic agent; and a polymeric covering layer disposed over saidtherapeutic agent containing layer, said polymeric covering layercomprising one or more polymers selected from (a) a block copolymercomprising at least two polymeric blocks A and B, wherein A is apolyolefin block and wherein B is a vinyl aromatic block, (b) a polymeror copolymer of lactic acid, (c) a polymer or copolymer of glycolicacid, and (d) a tyrosine-based polymer or copolymer, said polymericcovering layer having regions of a leachable material dispersed withinthe polymeric covering layer.
 2. The medical device of claim 1, whereinsaid polymeric covering layer comprises a block copolymer having atleast two polymeric blocks A and B, wherein A is a polyolefin block ofthe general formula —(CRR′—CH.sub.2).sub.n-, where R and R′ are linearor branched aliphatic groups or cyclic aliphatic groups and wherein B isa vinyl aromatic polymer block.
 3. The medical device of claim 1,wherein said polyolefin block comprises one or more monomers selectedfrom ethylene, butylene and isobutylene and wherein said vinyl aromaticpolymer block comprises one or more monomers selected from styrene and.alpha.-methylstyrene.
 4. The medical device of claim 1, wherein saidpolymeric covering layer comprises a copolymer of lactic acid andglycolic acid.
 5. The medical device of claim 1, wherein said polymericcovering layer comprises a tyrosine-derived polycarbonate.
 6. Themedical device of claim 1, wherein said therapeutic agent containinglayer is applied by dipping at least a portion of said medical deviceinto a solution comprising said high-molecular-weight therapeutic agent.7. The medical device of claim 1, wherein the medical device is selectedfrom a catheter, a balloon, a filter, a coil, a clip and a sling.
 8. Themedical device of claim 1, wherein the medical device is an intraluminalstent.
 9. The medical device of claim 8, wherein said intraluminal stentis a vascular stent.
 10. The medical device of claim 1, wherein saidhigh-molecular-weight therapeutic agent is selected from (a)polysaccharide therapeutic agents having a molecular weight greater than1,000; (b) polypeptide therapeutic agents having a molecular weightgreater than 10,000; and (c) polynucleotides having a molecular weightgreater tan 2,000.
 11. A medical device, at least a portion of which isinsertable or implantable into the body of a patient, said medicaldevice comprising: a polymeric layer comprising (a) a block copolymercomprising at least two polymeric blocks A and B and a removablecomponent, wherein A is a polyolefin block and wherein B is a vinylaromatic block or (b) a tyrosine-based polymer or copolymer and aremovable component comprising a leachable material ; and ahigh-molecular-weight therapeutic agent disposed below or within saidpolymeric layer, said polymeric covering layer having regions of theleachable material dispersed within the polymeric covering layer. 12.The medical device of claim 11, wherein said polymeric layer comprises ablock copolymer having at least two polymeric blocks A and B, wherein Ais a polyolefin block of the general formula —(CRR′—CH.sub.2).sub.n-,where R and R′ are linear or branched aliphatic groups or cyclicaliphatic groups and wherein B is a vinyl aromatic polymer block. 13.The medical device of claim 11, wherein said polyolefin block comprisesone or more monomers selected from ethylene, butylene and isobutyleneand wherein said vinyl aromatic polymer block comprises one or moremonomers selected from styrene and .alpha.-methylstyrene.
 14. Themedical device of claim 11, wherein said polymeric layer comprises atyrosine-derived polycarbonate.
 15. The medical device of claim 11,wherein said medical device is selected from a catheter, a balloon, afilter, a coil, a clip and a sling.
 16. The medical device of claim 11,wherein said medical device is an intraluminal stent.
 17. The medicaldevice of claim 16, wherein said intraluminal stent is a vascular stent.18. The medical device of claim 11, wherein said polynucleotide isplasmid DNA.
 19. The medical device of claim 11, wherein the removablecomponent is a leachable material.
 20. The medical device of claim 19,wherein the leachable material is selected from one or more of thefollowing: polyethylene glycols, polyalkylene oxides,polyhydroxyethylmethacrylates, polyvinylpyrrolidones, polyacrylamide andits copolymers, liposomes, proteins, peptides, salts, sugars,polysaccharides, polylactides, cationic lipids, detergents,polygalactides, polyanhydrides, polyorthoesters and their copolymers,and soluble cellulosics.
 21. The medical device of claim 20, wherein theleachable material is a salt.
 22. The medical device of claim 20,wherein the leachable material is a polyalkylene oxide selected from (a)polyethylene oxide and (b) copolymers of polyethylene oxide andpolypropylene oxide.
 23. The medical device of claim 11, wherein saidhigh-molecular-weight therapeutic agent is disposed below said polymericlayer.
 24. The medical device of claim 11, wherein saidhigh-molecular-weight therapeutic agent is disposed within saidpolymeric layer.
 25. The medical device of claim 11, wherein saidhigh-molecular-weight therapeutic agent is selected from polysaccharidetherapeutic agents having a molecular weight greater than 1,000;polypeptide therapeutic agents having a molecular weight greater than10,000; and polynucleotides having a molecular weight greater than2,000.